Description of issue / requirement to address

As a reactor modeller, I want the build of my reactor to be halted in some cases when performing a wire offset fails.

Having the fallback to a discretised offset is often useful, but in some cases, it's important to subsequent build steps that an offset produces a spline. The offset_wire function does produce a warning, but it's all too easy to miss (or ignore) this.

Proposed solution

Add a flag to offset_wire that prevents falling back to a discretised offset and instead raises a GeometryError.

Alternative solutions

No response

Additional Context

No response